Coaxial construction for power line carrier systems



I. GREEN April 26, 1932.

COAXIAL CONSTRUCTION FOR POWER LINE CARRIER SYSTEMS Filed April 21, 1931 Station 3 Stadium 3 INVENTOR Z. I Green Carrie.

(al I LEI @parzzzus Power Equq'oment Jtatiam 6 Carrier AZbpm-atus 'Statiom E Station I 2?; Station,

BY fi q ATTORNEY Patented Apr. 26, 1932 UNITED STATES PATENT OFFICE ESTILL I. GREEN, EAST ORANGE, NEW JERSET,ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK I COAXIAL CONSTRUCTION FOR POWER LINE CARRIER SYSTEMS Application filed April 21,

This invention relates to carrier transmission systems, and more particularly to carrier transmission systems which are superposed upon power networks.

In the use of carrier systems on power lines, considerable ditiiculty arises from the fact that the power circuit is generally part of a network of interconnecting lines, with tions.

frequent radiating spurs, paralleling circuits, etc. The high-frequency carrier system derived from a power line is therefore markedly different from a telephone line carrier circuit which proceeds directly from one terminal to another without intermediate connec- The complex nature of the power connections introduces undesirable impedance irregularities and reflection effects, and makes the characteristics of the carrier transmission circuit extremely erratic. For example, if it is desired to provide carrier transmission betweentwo stations and at an intermediate point in the power line connecting the stations there is a spur connection leading to another power station, the carrier frequency impedance presented by the spur line at the junction with the main line will vary widely with frequency. At'certain frequencies it may practically approach a short-circuiting condition, thereby preventing satisfactory transmission between the stations.

The power network is also unsatisfactory for carrier use because a particular carrier frequency which is applied to one part of the network is apt to spread over the entire system. Hence, a given frequency band can ordinarily be used only once in the-entire power network. Efforts have been made to obviate this difficulty by inserting in the power wires blocking high frequency impedances in the form of anti-resonant circuits or chokes. Such expedients, however, have a detrimental eifect upon the power circuit and, hence, have not been widely used.

Again, carrier transmission over power wires sulfers some limitation by reason of the interference which may be produced in telephone line carrier systems. Large amounts of power are required for the power line carrier system and owing to the unbal- 1931. Serial No. 531,764.

anced nature of the power circuit at high frequencies, the high frequency induction into adjacent telephone circuits is naturally large. Up to the present time this difiiculty has largely been avoided by employing different frequency ranges for the power line carrier systems and for telephone line carinterfering efi'ect upon-the carrier circuit of 5 such phenomena as corona discharge, arcing at defective insulators, etc., is partlcularly marked.

The purpose of the present invention is to provide means for surmounting the difficulties above noted by using coaxial conductors for power lines. As is well known, the modern tendency toward higher and higher voltages for power transmission has made the avoidance of corona discharge a very serious problem. Special power conductors are being designed to increase the corona limit, these ordinarily taking the form of a hollow conductor of large diameter and smooth surface. It is therefore proposed in accordance with the present invention to insert within these hollow conductors wires which are sup ported coaxially with respect to the power conductor by means of annular or diskshaped insulators. Thus, there will be derived at the nominal cost of a wire and some insulators, a coaxial circuit of a type which has been found extremely advantageous for high frequency transmission.

The invention will now be more fully understood from the following description, when read in connection with the accompanying drawings, in which Figure 1 illuscharge, etc., and Fig. 4 shows how one or more carrier systemsmay be applied t6 the concentric conductor transmission medium afforded by conductor Systems of the type shown in Figs. 2 and 3.

Referring to Fig. 1, a typical power circuit network is shown comprising a three-wire transmission line extending between stations A and B, at which stations power equipment 10 is provided as shown at P and P At an intermediate point a branch or spur power line of three conductors runs to another station C at which power equipment P is provided. Suppose, now, we have the problem of setting up'a signaling circuit such as a telephone circuit between stations A and B, and we attempt to solve this problem by connecting carrier terminal apparatus such as shown at C. and C to two of the power conductors through the usual coupling condensers so that one of the power conductors acts as a return for the other with regard to the carrier transmission system. At once the difliculty is presented that the carrier frequency impedance which the spur line presents at the junction with the main line will vary widely with frequency and at certain carrier frequencies will resemble a short circuit, thereby preventing satisfactory a0 transmission between stations A and B.

Such a carrier transmission system will also be subject to the various other dlifiCllltlQS which have already been outlined. r

Accordingly, it is proposed to use coaxial Jupower conductor arrangements for transmitting the carrier frequencies. Two types of conductors which may be employed in power lines for the purpose of increasing the corona discharge limit are shown in Figs. 2

1n and 3 respectively. These conductors-may be of copper or other suitable material. In Fig. 2 the outer conductor consists of a number of specially shaped wires 1010--10 which interlock by means of tongue and 4b groove arrangements to form what is practically a solid tube 20. This conductor may be used for power purposes without internal support. In Fig. 3 the outer or power conductor is composed of wires lOlG'-10 5B which are wedge-shaped or cuneiform in tric intervening between the conductors willv be air or other suitable gas whose dielectric constant is' approximately unity, so that there is substantially no power loss between i the conductors; .In the case of Fig. 3, the insulating spacers 22 may be used either instead of or in addition to the internal supporting rings 12 required for the outer wires.

By constructing the power conductors in this manner there is obtained a power line circuit which contains within itself a coaxial circuit for high frequency carrier transmission. This coaxial circuit may be terminated at any point merely by terminating the inner conductor as is shown, for'example, in F 4. Here the power circuit is made up of three hollow conductors 20, and 40, connected in three-wire form to power apparatus which may be branched offas shown at P... The power conductors which are shown as extending to stations A and B may also be considered to extend to a third station C at the left (not shown). For communication between stations A and B, outer tubular mem bers 20 and 20 may be associated with the conductor 20 as shown and the inner conductor 21 brought out at the two stations through these tubular outlets. The terminal carrier apparatus C at stations Aand similar apparatus C at station B, which is to be used for communication between stations A and B can then be connected to the conductors 21 and 20 through coupling condensers so that a concentric conductor system comprising conductors 20 and 21 is used for high-frequency transmission. Similarly, an inner concentrio conductor may be brought out through the outlet 20 as shown at 21 and terminal carrier apparatus G connected thereto for "elepl to prevent interference. Noise in the carrier circuit resultingfrom high frequency components'of the power frequencies would be very substantially reduced, owing to the fact that the power circuit and the carrier circuit would be, to a considerable extent, distinct from one another. high frequency waves employed for carrier transmission tend to concentrate along the outer surface of the inner conductor and the inner surface of the outer conductor, whereas the low frequency power currents will spread more or less throughout the crosssectional area of the copper forming the outer conductor. So far as skin effect applies to the power currents, it tends to concentrate the power waves at the outer surface of the outer conductor. The effects of corona discharge and other high frequency disturbances, so far as these are present, also tend to be concentrated at the outer surface of the outer conductor and consequently are shielded from the internal carrier transmission path.

Obviously, each conductors shown in Fig. 4 may be used for a different high frequency carrier circuit. Also, if desired, carrier circuits might be de rived from the power conductors in the usual way illustrated in Fig. 1 in addition to the carrier circuits afforded by the concentric conductor arrangements. The carrier currents for the circuit applied in accordance with the arrangements of Fig. 1 would flow on the outside of the power conductors while the carrier currents of the coaxial circuit would flow on the inside of these conductors and, hence, the two carrier systems would be effectively shielded from each other.

It will beobvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated, without departing from the spirit of the invention as defined in the following claims.

What is claimed is:

1. In a transmission system, hollow cylindrical conductors connected to form a transmission path for power currents, and an inner conductor arranged concentrically in at least one of said hollow conductors and connected to terminal carrier apparatus so that high frequency carrier currents may be transmitted, the inner conductor acting as a return for the outer at carrier frequencies.

2. In a transmission system, hollow cylindrical conductors connected to form a transmission path' for power currents between a number of stations greater than two, an inner conductor arranged concentrically in one of said conductors and having its ends brought out at two of said stations, carrier apparatus at each station connected to said hollow conductor and to said inner conductor, a second inner conductor concentrically arranged in the As is well known, theof the three hollow power same hollow conductor and extendingbetween one of said stations and a' third station, and carrier apparatus at each of said stations connected between the ends of said second con- .centric conductor and said hollow conductor.

3. In a transmission system, hollow cylindrical conductors connected to form a transmission path for power currents, an inner conductor arranged concentrically in at least one of said hollow conductors, insulating spacing material arranged along said inner conductor to maintain it in proper spacial relation with respect to said hollow conductor, and terminal carrier apparatus so connected to said inner conductor and said outer hollow conductor that the one acts as a return for the other in the transmission of high frequency carrier currents.

4. In a transmission system, hollow cylindrical conductors connected to form a transmission path for power currents between a number of stations greater than two, an inner conductor arranged concentrically in one of said, conductors and having its ends brought out at two of said stations, insulating spacing members arranged along said inner conductor to maintain it in proper spacial relationship with respect to said outer conductor, carrier apparatus at each station connected to said hollow conductor and to said inner conductor so that the one conductor acts as a return for the other for carrier transmission between the stations, a second inner conductor concentrically arranged in the same hollow conductor and extending between one of said stations and a third station, insulating spacing members arranged along said inner conductor to maintain it in proper spacial relationship with respect to said outer conductor, and carrier apparatus at each of said stations connected between the ends of said second concentric conductor and said hollow conductor so that the one conductor acts as a return for the other.

5. In a transmission system, hollow cylindrical conductors connected to form a transmission path for power currents, said conductors comprising a plurality of conductive strands so shaped that when arranged side by side and helically wound, their adjacent sides will fit each other to form a complete cylindrical structure, an inner conductor arranged concentrically in at least one of said hollow conductors, insulating spacers arranged along said insulating conductor for maintaining it in proper spacial relationship to said hollow conductor, and terminal carrier apparatus so connected to said hollow conductor and said inner conductor that the one conductor acts as a return for the other at carrier frequencies.

6. In a transmission system, hollow cylindrical conductors connected to form a transmission path for power currents between a number of stations greater than two,- each cylindrical conductor comprisin a plurality of conductive strands so shape that when arranged side by side and helically wound, their adjacent sides will fit each other to form a complete cylindrical structure, an inner conductor arranged concentrically in one of said conductors and having itsends brought out at two of said stations, insulating spacers arranged along said inner conductor for April, 1931.

maintaining to said hol ow conductor, carrier apparatus at each station connected to said hollow conductor and to said inner conductor so that the one acts as a return for the other for carrier transmission between said stations, a second inner conductor concentrically arranged in the same hollow conductor and extending between one of said stations and a third station, insulating spacers arranged along said second inner conductor for maintaining it in proper spacial relationship to said outer conductor, and carrier apparatus at each of said last mentioned stations connected to said second inner conductor and said outer conductor so that the one conductor acts as a return for the other for carrier transmission.

In testimony whereof, I have signed my name to this specification this 20th day of ESTILL I. GREEN.

it in proper spacial relationship 

